Biomedical Instrumentation Chapter 6 in Introduction to Biomedical Equipment Technology By Joseph Carr and John BrownSlide 2
Signal Acquisition Medical Instrumentation normally involves checking a flag off the body which is simple, changing over it to an electrical flag, and digitizing it to be broke down by the PC.Slide 3
Types of Sensors: Electrodes: obtain an electrical flag Transducers: procure a non-electrical flag (drive, weight, temp and so forth) and proselytes it to an electrical flagSlide 4
Active versus Passive Sensors: Active Sensor: Requires an outside AC or DC electrical source to control the gadget Strain gage, pulse sensor Passive Sensor: Provides it possess vitality or gets vitality from wonder being considered ThermocoupleSlide 5
Sensor Error Sources Error: Difference between measured esteem and genuine esteem.Slide 6
5 Categories of Errors: Insertion Error Application Error Characteristic Error Dynamic Error Environmental ErrorSlide 7
Insertion Error: Error happening while embeddings a sensorSlide 8
Application Error: Errors brought on by OperatorSlide 9
Characteristic Error: Errors inalienable to DeviceSlide 10
Dynamic Error: Most instruments are aligned in static conditions on the off chance that you are perusing a thermistor it requires investment to change its esteem. In the event that you read this esteem to rapidly a mistake will come about.Slide 11
Environmental Error: Errors brought on by environment warm, mugginessSlide 12
Sensor Terminology Sensitivity : Slope of yield trademark bend Δy/Δx; Minimum contribution of physical parameter will make a perceptible yield change Blood weight transducer may have an affectability of 10 uV/V/mmHg so you will see a 10 uV change for each V or mmHg connected to the framework.Slide 13
Output Input Which is more delicate? The left side one since you\'ll have a bigger change in y for a given change in xSlide 14
Ideal Curve Output Input Sensitivity Error Sensor Terminology Sensitivity Error = Departure from perfect slant of a trademark bendSlide 15
Sensor Terminology Range = Maximum and Minimum estimations of connected parameter that can be measured. In the event that an instrument can read up to 200 mmHg and the genuine perusing is 250 mmHg then you have surpassed the scope of the instrument.Slide 16
Sensor Terminology Dynamic Range: add up to scope of sensor for least to most extreme. Ie if your instrument can gauge from - 10V to +10 V your dynamic range is 20V Precision = Degree of reproducibility signified as the scope of one standard deviation σ Resolution = littlest discernible incremental change of information parameter that can be recognizedSlide 17
Xi Xo Accuracy = most extreme contrast that will exist between the genuine esteem and the demonstrated estimation of the sensorSlide 18
Offset Error Offset mistake = yield that will exist when it ought to be zero The trademark bend had similar touchy slant yet had a y block Output Input Offset Error Zero counterbalance blunderSlide 19
Linearity = Extent to which real quantify bended or adjustment bend leaves from perfect bend.Slide 20
Full Scale Input Ideal Measure Output Din(Max) Input Linearity Nonlinearity (%) = (Din(Max)/INfs) * 100% Nonlinearity is rate of nonlinear Din(max) = greatest info deviation INfs = most extreme full-scale inputSlide 21
Hysteresis = estimation of how sensor changes with information parameter in light of heading of progressSlide 22
Output = F(x) P F2 Input = x F1 B Q Hysteresis The esteem B can be spoken to by 2 estimations of F(x), F1 and F2. On the off chance that you are at point P then you achieve B by the esteem F2. In the event that you are at point Q then you achieve B by estimation of F1.Slide 23
F(t) Tolerance Band Tresponse 100% 70% Rising Response Time Ton Response Time Response Time: Time required for a sensor yield to change from past state to definite settle esteem inside a resilience band of right new esteem signified in red can be distinctive in rising and rotting headingsSlide 24
F(t) Tolerance Band Tresponse 100% 70% Rising Response Time Ton Response Time Constant: Depending on the source is characterized as the measure of time to achieve 0% to 70% of conclusive esteem. Ordinarily meant for capacitors as T = R C (Resistance * Capacitance) signified in BlueSlide 25
Response Time Convergence Eye Movement the internal turning of the eyes have an alternate reaction time than dissimilarity eye developments the outward turning of the eyes which would be the rot reaction time Tdecay F(t) Decaying Response Time Toff TimeSlide 26
F(x)* = hatchet + bx 2 +cx 4 + . . . +K F(x)* = hatchet + bx 3 +cx 5 + . . . +K Output F(x) Output F(x) F(x) = mx + K F(x) = mx + K Input X Input X Dynamic Linearity Measure of a sensor\'s capacity to take after fast changes in the information parameters. Contrast amongst strong and dashed bends is the non-linearity as portrayed by the higher request x termsSlide 27
Asymmetric = F(x) != |F(- x)| where F(x)* is topsy-turvy around straight bend F(x) then F(x) = hatchet + bx 2 +cx 4 + . . . +K balancing for K or you could accept K = 0 Symmetrical = F(x) = |F(- x)| where F(x) * is symmetric around straight bend F(x) then F(x) = hatchet +bx 3 + cx 5 +. . . + K balancing for K or you could accept K =0 Dynamic LinearitySlide 28
Av = Vo/Vi 1.0 Frequency ( w ) radians every second Frequency Response of Ideal and Practical System When you take a gander at the recurrence reaction of an instrument, in a perfect world you need a wideband level recurrence reaction.Slide 29
Av = Vo/Vi 1.0 0.707 FL FH Frequency ( w ) radians every second Frequency Response of Ideal and Practical System by and by, you have weakening of lower and higher frequencies FL and FH are known as the –3 dB focuses in voltage frameworks.Slide 30
Examples of Filters Ideal Filter has sharp shorts and a level pass band Most channels lessen upper and lower frequencies Other channels constrict upper and lower frequencies and are not level in the pass bandSlide 31
Electrodes for Biophysical Sensing Bioelectricity: actually happening current that exists since living beings have particles in different amountsSlide 32
Electrodes for Biophysical Sensing Ionic Conduction: Migration of particles decidedly and contrarily charge atoms all through an area. To a great degree nonlinear yet in the event that you restrain the area can be viewed as straightSlide 33
Electrodes for Biophysical Sensing Electronic Conduction: Flow of electrons affected by an electrical fieldSlide 34
Bioelectrodes: class of sensors that transduce ionic conduction to electronic conduction so can handle by electric circuits Used to obtain ECG, EEG, EMG, and so forthSlide 35
Bioelectrodes 3 Types of cathodes: Surface (in vivo) outside body Indwelling Macroelectrodes (in vivo) Microelectrodes (in vitro) inside bodySlide 36
Bioelectrodes Electrode Potentials: Skin is electrolytic and can be displayed as electrolytic arrangements Metal Electrode Electrolytic Solution where Skin is electrolytic and can be demonstrated as salineSlide 37
Electrodes in Solution Have metallic anode submerged in electrolytic arrangement once metal test is in electrolytic arrangement it: Discharges metallic particles into arrangement Some particles in arrangement join with metallic terminals Charge slope constructs making a potential distinction or you have a cathode potential or ½ cell potentialSlide 38
Electrodes in Solution 2 cells An and B, A has 2 positive particles And B has 3 positive particles subsequently have a Potential contrast of 3 –2 = 1 where B is more positive than An A ++ B +++Slide 39
Electrodes Two responses occur at terminal/electrolyte interface: Oxidizing Reaction: Metal - > electrons + metal particles Reduction Reaction : Electrons + metal particles - > MetalSlide 40
Vae Metal A Vbe Metal B Electrolytic Solution Electrodes Electrode Double Layer: framed by 2 parallel layers of particles of inverse charge brought about by particles relocating from 1 side of locale or another; ionic contrasts are the wellspring of the cathode potential or half-cell potential (Ve).Slide 41
Electrodes If metals are diverse you will have differential potential some of the time called a terminal counterbalance potential. Metal A = gold Vae = 1.50V and Metal B = silver Vbe = 0.8V then Vab = 1.5V – 0.8 V = 0.7V (Table 6-1 in book page 96) Vae Metal A Vbe Metal B Electrolytic SolutionSlide 42
Electrodes Two general classifications of material mixes: Perfectly energized or flawlessly nonreversible cathode: no net exchange of charge crosswise over metal/electrolyte interface Perfectly Nonpolarized or splendidly reversible terminal: unhindered exchange of charge between metal anode and the cathode Generally select a reversible cathode, for example, Ag-AgCl (silver-silver chloride)Slide 43
R t = inner resistance of body which is low Vd = Differential voltage Vd Rsa and Rsb = skin resistance at terminal An and B Electrode A C1a Vea + - Rsa Cellular Resistance R1a Rc - Vo Mass Tissue Resistance R t Vd Cellular Potentials + Electrode B C1b Veb + - Rsb R1b Ionic Conduction Electronic Conduction R1A and R1B = resistance of cathodes C1A and C1B = capacitance of terminalsSlide 44
Electrode Potentials cause recording Problems ½ cell potential ~ 1.5 V while biopotentials are typically 1000 times less (ECG = 1-2 mV and EEG is 50 uV) in this way have a gigantic contrast between DC cell potential and biopotential Strategies to conquer DC part Differential DC speaker to get flag hence the DC segment will counteract Counter Offset-Voltage to wipe out half-cell potential AC couple contribution of enhancer (DC won\'t go through) ie capacitively couple the flag into the circuitSlide 45
Electrode Potentials make recording Problems Strategies beat DC segment Differential DC intensifier to obtain flag th
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